Automatic transmission with lock-up clutch

ABSTRACT

In an automatic transmission equipped with a lock-up clutch (6) capable of transmitting engine power to the automatic transmission (1) directly or via a torque converter (2), the automatic transmission has sensors (11, 12) for detecting an input rotational speed and an output rotational speed of the transmission, a control system including a shift start determination step (66) for judging start of a shift by comparing a ratio of the input rotational speed to the output rotational speed with a gear ratio prevailing prior to a shift and a shift end determination step (68) for judging end of a shift by comparing the ratio of the input rotational speed to the output rotational speed with a gear ratio prevailing after a shift, and a lock-up solenoid (10) responsive to output signals from the shift start determination step and shift end determination step for releasing the lock-up clutch (6) during a shift. Thus, proper control of the lock-up clutch at the time of a gear shift can be carried out even in the same type of transmission and even under all shift conditions, and shock such as racing of the engine or a shift executed with the lock-up clutch in the engaged state can be prevented.

DESCRIPTION

1. Technical Field

This invention relates to an automatic transmission with a lock-upclutch in which the lock-up clutch is released during a shiftingoperation in order to improve the feeling of the shifting operation.

2. Background Art

In a system having a lock-up clutch arranged within a torque converterconnected between an engine and an automatic transmission fortransmitting the power of the engine directly to the transmission underpredetermined conditions, the lock-up clutch generally is engaged ordisengaged based on a shift pattern set for each range of gearpositions. More specifically, in order to improve fuel economy, controlis exercised in such a manner that the lock-up clutch is released totransmit engine power to the transmission via the torque converter ifthrottle opening and vehicle velocity are in a torque conversion regionof a shift pattern, and in such a manner that the lock-up clutch isengaged to transmit motor power directly to the transmission if throttleopening and vehicle velocity are in a lock-up region of the shiftpattern.

However, in a shift pattern set for each range of gear position, lock-upregions adjoin about shift points at the boundaries. Therefore, when theaccelerator pedal is depressed by a great amount so that the automatictransmission is operating under a large throttle opening, gears areshifted while the locked up state remains in effect. As a result, alarge speed-change shock is produced.

Conventionally, the system shown in FIG. 8 is employed in order toeliminate speed-change shock. Specifically, in an electronic controlunit of the automatic transmission, a shift is determined at time t₁and, after an elapsed time of T₁, a shift signal is delivered to a shiftsolenoid at a time t₂. However, owing to a response delay in thehydraulic system, the actual shift starts upon passage of a time T₂.Accordingly, the time period T₂ is preset, the lock-up clutch isreleased at a time t₃ to prevent the occurrence of speed-change shock,and the lock-up clutch is re-engaged at a time t₄, at which the shiftends, upon elapse of a time period T₃. The time periods T₁, T₂, T₃involving the shift signal and the signals for engaging and disengagedthe lock-up clutch are stored in advance by a timer within a computer,and control of the gear shift and lock-up clutch timing is performingbased on the timer.

As indicated in Japanese Patent Application Laid-Open No. 61-27365, asystem has been disclosed in which engine rotational speed followingissuance of a shift command is monitored and the start of a shift isdetermined when the rate of change in rotational speed surpasses a setvalue. In other words, the amount of engine racing at the time of a gearshift is fed back and the lock-up clutch is released when the integratedvalue of the feedback exceeds a set value. In other words, as shown inFIG. 9, at the moment t₂ a rate of change-dN_(E) /dt in enginerotational speed surpasses a set value .sub.Δ N following an instant t₁at which a shift command is issued, lock-up is suspended by an outputduty of 0% and the suspension continues for a set time period T1. If thelock-up region still prevails after this time, the output duty D isabruptly made D_(A) % and is then gradually raised to 100% at a slopeα/T2, so that the torque converter can be returned to the lock-up state.By deciding the set value .sub.Δ N of the rate of change in enginerotational speed on the basis of the rate of change in engine rotationalspeed after issuance of the shift command, namely by setting .sub.Δ N toa value obtained by multiplying the maximum value thereof by a safetyfactor β, speed-change shock due to suspension of lock-up is prevented.

Further, as illustrated in Japanese Patent Application Laid-Open No.61-27364, a system is disclosed in which the lock-up clutch is releasedupon discriminating the degree to which a shift has progressed afterissuance of a shift command using the rotational speed of the torqueconverter prior to the shift and the gear ratio prior of the shift asreferences. More specifically, as shown in FIG. 10, timing for startingcontrol of lock-up suspension is decided depending upon whether therotational speed N of the torque converter has attained a referencevalue N_(c) obtained based upon the rotational speed N_(b) of the torqueconverter at the start of a shift.

However, in the system in which timing control of the shift and lock-upclutch is carried out based on the timer, once the timer has been set,the set time is the same in transmissions of the same type and under allshift conditions. Therefore, temporal disparaties relating to shift andlock-up control arise due, for example, to differences in piston strokein the friction devices and differences in orifice diameter in thehydraulic circuitry. Also, depending upon changes with time, shock suchas racing of the engine or a shift executed with the lock-up clutch inthe engaged state occur.

The system disclosed in the aforementioned Japanese Patent ApplicationLaid-Open No. 61-27364 also has a problem. Depending upon the travellingconditions of the vehicle (e.g. whether the vehicle is travelling on anupgrade or downgrade or a hauling a load, etc.), the state of vehicleacceleration changes even for the same throttle opening, enginerotational speed and torque converter rotational speed. As a result, theinput rotational speed of the torque converter during a shiftingoperation changes is various ways according to the travellingconditions. When such is the case, it is difficult to detect the startof a shift and the progress of the shift based solely on the inputrotational speed of the torque converter or the like.

Furthermore, owing to disparities in oil temperature and engagingelements, there is a response delay in making a transition from thefully engaged state of the lock-up clutch so that the clutch is notalways released instantaneously even though a lock-up release signal isissued in the course of a gear shift. Thus, there is the possible thattransmission shock will occur. In addition, fully releasing the lock-upclutch during a shift will not completely suppress engine racing andspeed-change shock, particularly in a region where torque converter slipis large, even if the timing of the release is synchronized to the shiftby the above-described conventional method.

Also, with regard to engagement of the lock-up clutch when a shift ends,it is difficult to prevent the occurrence of speed-change shock causedby a disparity in the moment a shift ends since the time setting in theabove-described system is made by the timer.

The present invention seeks to solve the foregoing problems and itsobject is to provide an automatic transmission having a lock-up clutchin which it is possible to correctly judge the start and end of a gearshift based on the input rotational speed and output rotational speed ofthe automatic transmission, with the lock-up clutch being controlled byfeeding back signals indicative of the judgments made, thereby improvingthe feeling of the gear shift.

DISCLOSURE OF THE INVENTION

In order to attain the foregoing object, an automatic transmission witha lock-up clutch according to the present invention is characterized inthat, in an automatic transmission equipped with a lock-up clutchcapable of transmitting engine power to the automatic transmissiondirectly or via a torque converter, the automatic transmission comprisesdetecting means for detecting an input rotational speed and an outputrotational speed of the transmission, shift start determination meansfor judging start of a shift by comparing a ratio of the inputrotational speed to the output rotational speed with a gear ratioprevailing prior to a shift, shift end determination means for judgingend of a shift by comparing the ratio of the input rotational speed tothe output rotational speed with a gear ratio prevailing after a shift,and a lock-up solenoid responsive to output signals from the shift startdetermination means and shift end determination means for releasing thelock-up clutch during a shift. In another aspect, the automatictransmission is characterized by having a lock-up solenoid responsive tooutput signals from the shift start determination means and shift enddetermination means for controlling the lock-up clutch so that thelock-up clutch is capable of assuming a standy state, sweep state orslip state during a shift.

Thus, in accordance with the invention, the lock-up clutch is controlledby comparing the ratio of the input rotational speed of the automatictransmission to the output rotational speed thereof during a shift withthe gear ratio before the shift, and accurately determining thebeginning and end of the shift. Therefore, proper control of the lock-upclutch at the time of a gear shift can be carried out even in the sametype of transmission and even under all shift conditions, and shock suchas racing of the engine or a shift executed with the lock-up clutch inthe engaged state can be prevented.

In a case where the lock-up clutch is controlled so as to assume astandby state, sweep state or slip state between the start and end of agear shift, the lock-up clutch can be made to respond immediately andcan be made to engage or disengage smoothly to further enhance thefeeling of the gear shifting operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view of an automatic transmission with lock-upclutch in accordance with the present invention;

FIG. 2 is a block diagram illustrating a first embodiment of a controlsystem according to the present invention;

FIGS. 3 and 4 are views illustrating an embodiment of the flow throughwhich the lock-up clutch of the invention is control

FIGS. 5 and 6 views illustrating an embodiment of the flow through whichthe lock-up clutch of the invention is controlled; and

FIG. 7 is a view for describing the operating states of the lock-upclutch.

FIGS. 8 -10 show prior systems for eliminating or absorbing speed changeshock.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, an automatic transmission 1 has a torque converter 2 as afirst stage. The torque converter 2 is equipped with a pump impeller 4,a turbine runner 5 and a lock-up clutch 6 within a housing 3. In thetorque conversion region of a shift pattern, the lock-up clutch 6 isfreed from the housing 3 so that power from the engine is transferred tothe automatic transmission 1 via the pump impeller 4 and turbine runner5. In the lock-up region, the lock-up clutch 6 is engaged with thehousing 3, so that the power from the engine is transferred to theautomatic transmission 1 via the housing 3.

The automatic transmission 1 comprises a well-known planetary gear groupand a friction device (not shown) for fixing or freeing each of theelements of the planetary gears. Travel is made possible in the optimumgear by selectively actuating the elements of the friction deviceautomatically via a hydraulic circuit 7 in dependence upon thetravelling state of the vehicle. The hydraulic circuit 7 is providedwith a shift solenoid (No. 1) 8, a shift solenoid (No. 2) 9 and alock-up solenoid 10. On the basis of a combination of on/off signalsapplied to the shift solenoid (No. 1) 8 and shift solenoid (No. 2) 9,the elements of the aforementioned friction device are selectivelyactuated to shift speeds. The lock-up solenoid 10 is a duty solenoidcontrolled via computer by e.g. a 50 Hz ON-OFF signal. By changing theproportion of the ON time (the duty ratio) of the ON-OFF signal, it ispossible to control the engagement, slip and release of the lock-upclutch 6. The solenoids 8, 9 and 10 are controlled by an electroniccontrol unit 14 on the basis of signals from a sensor which senses theinput rotational speed of the automatic transmission, a sensor 12 whichsenses the output rotational speed of the automatic transmission, and anengine throttle opening sensor 13. The electronic control unit 14 issupplied with a constant voltage from a battery 15.

An embodiment of the electronic control unit 14 shown in FIG. 1 will nowbe described with reference to FIG. 2. The signals from the automatictransmission input rotational speed sensor 11, output rotational speedsensor 12 and engine throttle opening sensor 13 are inputted to a CPU 17through an input signal converter circuit 16, and the CPU 17 is suppliedwith the constant voltage from the battery 15 through a constant-volagecircuit 18. The CPU 17 has shift start command determination unit 19, ashift start determination unit 20, a shift end determination unit 21 anda duty output determination unit 22. A control program and variousdetermination tables are stored in a ROM 23, and a RAM 24 is providedwith a working area. On the basis of the control program anddetermination tables, the CPU 17 performs predetermined processing andmakes decisions based on the input signals and outputs control signalsto the shift solenoid (No. 1) 8, shift solenoid (No. 2) 9 and lock-upsolenoid 10 via an output circuit 25.

The flow of processing executed by the CPU 17 will now be described withreference to FIGS. 3 and 4.

The main routine of FIG. 3 is executed at all times during travelling ofthe vehicle. When the program is started at a step 61, it is determinedat a step 62 whether a shift start command has been issued. The shiftstart command is issued in a separate gear shift program. A shift flagFSFT is set to 0 or 01 depending upon whether the present travellingconditions are such that there is a change in a shift region in theshift pattern stored in the ROM. If a shift start command has not beenissued, the program proceeds to a step 64. If this command has beenissued, the program proceeds to a step 63.

At the step 63, the shift flag FSFT is set to 01 and a gear ratio GRBbefore a shift and a gear ratio GRN after a shift are read in from theROM. Next, it is determined at a step 64 whether the shift flag FSFT is0. If FSFT is 0, then the program proceeds to a step 70. If FSFT is not0, the program proceeds to a step 65, at which the input rotationalspeed Ni and output rotational speed No of the transmission are read inand the present gear ratio GR=Ni/No of the transmission is calculated.Next, a step 66 calls for a determination as to whether the present gearratio GR resides within a fixed range of ±δ₁ of the gear ratio GRBbefore a shift. If the GR does reside within this fixed range, it isjudged that a shift has not yet started and the program proceeds to astep 68. When the present gear ratio GR falls outside the fixed range ofthe gear ratio GRB before a shift while this routine is being repeated,the program proceeds to a step 67, at which it is judged that a shifthas started and the shift flag FSFT is set to 02.

The step 68 calls for a determination as to whether the present gearratio GR resides within a fixed range of ±δ₂ of the gear ratio GRN aftera shift. If Gr is outside this fixed range, it is judged that a shifthas not yet ended and the program proceeds to the step 70. When thepresent gear ratio GR falls within the fixed range of the gear ratio GRNafter a shift while this routine is being repeated, the program proceedsto a step 69, at which it is judged that a shift has ended and the shiftflag FSFT is set to 00. Thereafter, the above-described routine isexecuted repeatedly.

The routine of FIG. 4 is called in the main routine or is executed withan interrupt at fixed time intervals determined by a timer. First, it isdetermined at a step 71 whether the lock-up region of a shift pattern isprevailing. If the prevailing region is not the lock-up region, then theprogram proceeds to a step 72, at which the lock-up clutch is maintainedin a completely disengaged state. If the lock-up region is prevailing,then the program proceeds to a step 73, at which it is determinedwhether the transmission flag FSFT is 01. If FSFT is 01, namely if thestart of a shift has been determined, the program proceeds to a step 72,at which a signal releasing the lock-up clutch is outputted to thelock-up solenoid. If it has been determined that a shift has notstarted, the program proceeds to a step 74, at which a signal forengaging the lock-up clutch is outputted to the lock-up solenoid. Thisis followed by a step 75, at which it is determined whether the shiftflag FSFT is 03. If FSFT is not 03, namely if a shift has not ended,then the abovementioned routine is executed when called within the nextcycle of the main routine or when an interrupt is generated. When ashift ends, the program proceeds to a step 76, at which the shift flagFSFT is made 0. Thereafter, the foregoing routine is executedrepeatedly.

Another embodiment illustrated in FIGS. 5 and 6 will now be described.The routine of FIG. 5 is executed at all times while the vehicle istravelling. When the program is started at a step 31, it is determinedat a step 32 whether the shift flag FSFT, which is set to 0 if a shiftstart command has not been issued, is not 0. The shift start command isissued in a separate shift program. The shift flag FSFT is set to 0 or01 depending upon whether the present travelling conditions are suchthat there is a change in a shift region in the shift pattern stored inthe ROM. If the shift flag FSFT is 0, namely if a shift start commandhas not been issued, the program proceeds to a step 38. If this commandhas been issued, the program proceeds to a step 33.

At step 33, the input rotational speed Ni and output rotational speed Noof the transmission are read in and the present gear ratio GR=Ni/No ofthe transmission is calculated. The next step 34 calls for adetermination as to whether the present gear ratio GR is equal to thegear ratio GRB before a shift. If it is equal, it is judged that a shifthas not yet started and the program proceeds to a step 36. When thepresent gear ratio GR becomes non-equal to the gear ratio GRB before ashift while this routine is being repeated, the start of a shift isdetermined to have occurred at a step 35, the shift flag FSFT is made 02and SW, described below, is made 0.

A step 36 calls for a determination as to whether the present gear ratioGR is equal to the gear ratio GRN after a shift. If it is not equal, itis judged that a shift has not yet ended and the program proceeds to astep 38. When the present gear ratio GR becomes equal to the gear ratioGRN after a shift while this routine is being repeated, the end of ashift is determined to have occurred at a step 37, the shift flag FSFTis made 03 and a value BD is inserted in SW, described below.

The decisions that a shift has started and ended will now be describedin detail. In the case of an upshift, the decision that a shift has beenstarted is made when Ni/No≦K1×GRB holds (where K1 is a coefficient ofe.g. 0.9), and the decision that a shift has been ended is made whenNi/No≦K2×GRN holds (where K2 is a coefficient of e.g. 1.1). In the caseof a downshift, the decision that a shift has been started is made whenNi/No≦K1×GRB holds (where K1 is a coefficient of e.g. 1.1), and thedecision that a shift has been ended is made when Ni/No≦K2×GRN holds(where K2 is a coefficient of e.g. 0.9).

At the step 38, a standby duty ratio PD, a slip duty ratio SD, a sweepratio 3SWP1 for when the lock-up clutch is directed toward the released(OFF) state, a sweep ratio SWP2 for when the lock-up clutch is directedtoward the engaged (ON) state, and an initial duty BD for a case wherethe lock-up clutch is directed toward the engaged state, all of whichare set for every throttle opening TH, are read in. These numericalvalues are stored beforehand in the ROM 23 in the form shown in table39. The program proceeds from the step 38 to a step 40 and theabove-described loop is repeated, whereby various input information isconstantly read in.

The routine of FIG. 6 is executed with an interrupt at fixed timeintervals determined by a timer. First, it is determined at a step 50whether the shift flag FSFT is 0. If FSFT is 0, namely if a shift startcommand has not been issued, the program proceeds to a step 51, at whichit is determined whether the lock-up region of a shift pattern isprevailing. If the prevailing region is not the lock-up region, theprogram proceeds to a step 60, at which the lock-up clutch is maintainedin the completely disengaged state. If the lock-up region is prevailing,the program proceeds to a step 56, at which the lock-up clutch isengaged at a sweep ratio directing the clutch toward the engaged (ON)state, as will be described below.

If FSFT is not 0 at the step 50, namely if the shift command has beenissued, it is determined at a step 52 whether the prevailing region isthe lock-up region of a shift pattern. If it is not the lock-up region,the program proceeds to a step 60, at which the released state of thelock-up clutch is maintained and the usual shift program is executed. Ifthe lock-up region is prevailing, then the state of the shift flag FSFTis discriminated at a step 53.

The program proceeds to a step 54 if the shift flag FSFT illustrated inFIG. 5 is found to be 01 at the step 53, to a step 55 if the flag isfound to be 02, and to a step 56 if the flag is found to be 03. When thestep 54 is selected, output duty ratio ODR is made the standby dutyratio PD corresponding to the throttle opening. This is followed by astep 61, a signal is delivered to the lock-up solenoid to, whereby thelock-up clutch is made to standby in a state in which it may be actuatedin the release direction at any time.

If the step 55 is selected, namely if start of a shift has beendetermined, the sweep ratio SWP1 for when the lock-up clutch is directedtoward the released (OFF) state is read in, SW=SW+SWP1 is evaluated andthe output duty ratio ODR is made PD+SW. This is followed by a step 57,at which it is determined whether ODR has attained the slip duty ratioSD. If SD has not been attained, a signal is delivered as the outputduty ratio ODR to the lock-up solenoid at the step 61, so that thelock-up clutch is swept in the release direction. Each time this loop isexecuted at a fixed time interval, the sweep ratio SWP1 is added toperform the operation SW=SW+SWP1. When ODR attains the slip duty ratioSD at the step 57, the program proceeds to a step 58 at which, when thenext cycle of the routine is executed, the operation SW=SW-SWP1 isperformed in order to maintain the relation ODR=SD. Thereafter, theoutput duty ratio signal ODR=SD is delivered to the lock-up solenoid toplace the lock-up clutch in the predetermined slip state.

If the step 56 is selected, namely if it is determined that a shift hasended, the sweep ratio SWP2 for when the lock-up clutch is directedtoward the engaged (ON) state is read in, SW=SW+SW2 is evaluated and theoutput duty ratio ODR is made SD+SW. This is followed by a step 59, atwhich it is determined whether ODR has attained the standby duty ratioPD. If PD has not been attained, a signal is delivered as the outputduty ratio ODR to the lock-up solenoid at the step 61, so that thelock-up clutch is swept in the engaging direction. Each time this loopis executed at a fixed time interval, the sweep ratio SWP2 is added toperform the operation SW=SW+SWP2. When ODR attains the standby dutyratio PD at the step 59, the program proceeds to a step 62 at which thelock-up clutch is placed in the fully engaged state.

The operation of the lock-up clutch will now be described with referenceto FIG. 7. At a time t₁, a shift is determined to have taken place, theoutput duty ratio ODR is made the standby duty ratio PD corresponding tothe throttle opening, and a signal is delivered to the lock-up solenoid,whereby the lock-up clutch is made to standby in a state in which it maybe operated in the release direction at any time. Next, at a time t₂which follows the time t₁ by a period T1, a shift signal is applied tothe shift solenoid, though an actual shift does not yet take place dueto a delay in the response of the hydraulic system. When the start of ashift is determined to have taken place at the step 34 in FIG. 5, asignal is delivered to the lock-up solenoid at the output duty ratio ODRdescribed in connection with the step 55 of FIG. 6, whereby the lock-upclutch is swept in the release direction. When the output duty ratioattains the slip duty ratio SD, the output duty ratio signal ODR =SD isdelivered to the lock-up solenoid, whereby the lock-up clutch is placedin the predetermined slip state. Thereafter, when the end of a shift isdetermined at the step 36, the lock-up clutch is swept in the engagingdirection from the initial duty ratio BD. When the standby duty ratio PDis attained, the lock-up clutch is placed in the fully engaged state. Inthe case of the embodiment described in connection with FIGS. 3 and 4,the arrangement is such that the lock-up clutch is released by makingthe output duty ratio of the lock-up solenoid 0% immediately after thestart of a shift is determined, and engaged by making the output dutyratio of the lock-up solenoid 100% immediately after the end of a shiftis determined.

INDUSTRIAL APPLICABILITY

The automatic transmission with the lock-up clutch in accordance withthe invention is installed in a vehicle and is applied for the purposeof enhancing the feeling of a gear shift operation.

What is claimed is:
 1. An automatic transmission equipped with a lock-upclutch capable of transmitting engine power to the automatictransmission directly or via a torque converter, characterized bycomprising: detecting means for detecting an input rotational speed andan output rotational speed of the transmission, shift startdetermination means for judging start of a shift by comparing a ratio ofthe input rotational speed to the output rotational speed with a gearratio prevailing prior to a shift, shift end determination means forjudging end of a shift by comparing the ratio of the input rotationalspeed to the output rotational speed with a gear ratio prevailing aftera shift, and a lock-up solenoid responsive to output signals from saidshift start determination means and said shift end determination meansfor releasing the lock-up clutch during a shift.
 2. An automatictransmission equipped with a lock-up clutch capable of transmittingengine power to the automatic transmission directly or via a torqueconverter, characterized by comprising: detecting means for detecting aninput rotational speed and an output rotational speed of thetransmission, shift start determination means for judging start of ashift by comparing a ratio of the input rotational speed to the outputrotational speed with a gear ratio prevailing prior to a shift, shiftend determination means for judging end of a shift by comparing theratio of the input rotational speed to the output rotational speed witha gear ratio prevailing after a shift, and a lock-up solenoid responsiveto output signals from said shift start determination means and saidshift end determination means for controlling the lock-up clutch so thatthe lock-up clutch is capable of assuming a standby state, sweep stateor slip state during a shift.